Illegal Waste Dumps and Water Quality: Environmental and Logistical Challenges for Sustainable Development—A Case Study of the Ružín Reservoir (Slovakia)

Abstract

The aim of the article is to highlight the increasing environmental burden on aquatic ecosystems in Slovakia due to continuous pollution from municipal, industrial and agricultural sources. Laboratory analyses have shown alarming exceedance of the limit values of contaminants, with nitrate nitrogen (NO₃⁻) reaching 5.8 mg/L compared to the set limit of 2.5 mg/L and phosphorus concentrations exceeding the permissible values by a factor of five, thereby escalating the risk of eutrophication and loss of ecological stability of the aquatic ecosystem. The accumulation of heavy metals is also a problem—lead (Pb) concentrations reach up to 9.7 μg/L, which exceeds the safe limit by a factor of ten. Despite the measures implemented, such as scum barriers, there is continuous contamination of the aquatic environment, with illegal waste dumps and uncontrolled runoff of agrochemicals playing a significant role. The research results underline the critical need for a more effective environmental policy and more rigorous monitoring of toxic substances in real time. These findings highlight not only the urgency of more effective environmental policy and stricter real-time monitoring of toxic substances, but also the necessity of integrating environmental logistics into the design of sustainable solutions. Logistical approaches including the optimization of waste collection, coordination of stakeholders and creation of infrastructural conditions can significantly contribute to reducing environmental burdens and ensure the continuity of environmental management in ecologically sensitive areas.

1. Introduction

Aquatic ecosystems are an essential part of the global environmental system, and their quality reflects the level of anthropogenic pressure. Despite technological progress and increasing environmental regulations, the degradation of surface waters remains one of the most urgent environmental problems today. The consequences of pollution are multi-layered; they include the disruption of biochemical cycles, the disappearance of biodiversity, the contamination of drinking water and long-term negative impacts on human health. The most significant factors contributing to the deterioration of water quality include uncontrolled waste dumps, which become persistent sources of environmental toxins, including heavy metals, persistent organic matter and pathogenic microorganisms [1].

Improper waste management is particularly problematic in areas with poorly regulated environmental management, where waste dumps are created near watercourses and are contaminated over a long period of time through surface and underground transport of substances. The chemical composition of leachate from waste dumps is variable and depends on meteorological conditions, geological bedrock and waste composition [2]. Similar challenges have been identified in a global context, with research by Molenda and Chmura (2012) in Cameroon documenting a significant deterioration in groundwater quality due to municipal waste dumps, while an increased incidence of diseases caused by toxic substances has also been demonstrated [3]. In Poland, Rabuffetti et al. (2024) pointed to the negative impact of industrial waste dumps on the quality of surface water and drinking water sources [4].

In addition to direct chemical impacts, waste dumps have broader environmental and hydrological consequences that lead to the degradation of functional ecosystem processes. Research by Bora et al. (2023) in the Black Sea region confirms that waste in coastal areas causes secondary pollution and reduces the biodiversity of aquatic organisms [5]. Wei Qiang et al. (2022) identified hazardous concentrations of heavy metals in river sediments in China, with their origin related to municipal and industrial wastewater [6].

However, illegal waste dumps do not only pose an environmental threat, but also a serious health risk. Research by Mazza et al. (2015) in Campania, Italy, highlighted a statistically significant correlation between the dumping of toxic waste and the increased incidence of respiratory diseases and oncological diagnoses [7]. These findings demonstrate the need for more robust legislative scrutiny and more effective monitoring mechanisms.

Slovakia is one of the countries in Central Europe where illegal dumping represents a significant environmental challenge. The situation is particularly serious in the catchment area of the Hornád and Hnilec rivers, where accumulated pollution escalates during intense rainfall and floods, leading to an accelerated transport of contaminants into the aquatic ecosystem. The increase in plastic waste, increased concentrations of heavy metals and the increase in microplastics in these streams indicate an increasing level of anthropogenic impact and reduce the ability of aquatic ecosystems to maintain a self-cleaning function [8].

One of the most critical environmental points in Slovakia is the Ružín water reservoir, which annually accumulates large amounts of waste washed away from the upper streams. Plastic waste, especially PET bottles and municipal packaging, dominates among contaminants and the amount increases exponentially during extreme hydrological events [9]. This situation requires a multidisciplinary approach that includes the elimination of illegal waste dumps, waste management reform and the implementation of preventive measures.

Scientific evidence clearly indicates that the pollution of waterways by illegal waste dumps not only causes chemical contamination, but also leads to widespread environmental and health impacts. Bhuyan et al. (2023) documented the presence of toxic metals such as lead, cadmium and mercury in the sediments of the Bharal River in India, which significantly affected the ecological balance and biodiversity [10]. Rath et al. (2005) identified excessive concentrations of nitrogen compounds and phosphorus in the sediments of the Brahmani and Nandira rivers, exacerbating eutrophication and endangering biodiversity [11].

In the case of Ružín, the main problem is the absence of effective waste collection and low environmental awareness in the Hornád and Hnilec river basins. The results of research by Gohain and Bordoloi (2021) point to a similar pattern of pollution in India, where municipal waste significantly affects the quality of water bodies [12]. Long-term exposure to contaminants leads to a gradual deterioration in water quality, loss of ecosystem services and negative socio-economic consequences [13,14].

In this context, it is essential to consider the dynamics of natural processes that ensure the flow, redistribution and availability of water, sediments and nutrients within the landscape. These processes, which inherently occur in hydrological and ecological systems, are critical for maintaining the sustainability of ecosystem services and the overall functionality of the aquatic environment. When these processes are disturbed, for example due to illegal waste dumps or diffuse pollution, it results not only in a decline in water quality but also in the loss of the landscape’s capacity to sustain natural environmental flows and preserve ecological balance [15,16].

This study provides a comprehensive, site-specific assessment of the environmental impacts of illegal waste dumping on water quality in the Ružín reservoir area—a critical but scientifically underexplored region of Central Europe. Unlike previous studies that have focused primarily on urban streams or general pollution sources, this research integrates field monitoring, laboratory analysis and hydrological context to more precisely trace the origin, pathways and risks associated with uncontrolled waste disposal. By mapping the spatial distribution of contaminants and identifying ecological thresholds, the study deepens the understanding of the cumulative effects of environmental stress in vulnerable freshwater ecosystems. The findings offer not only scientific insights but also practical foundations for the development of targeted and sustainable water resource management strategies. Moreover, the acquired knowledge is transferable to other similarly affected catchments in Central Europe, positioning the Ružín basin as a representative model area.

2. Materials and Methods

This chapter presents a methodological approach used in the assessment of the environmental condition of the Ružín water reservoir. Particular attention was paid to the analysis of hydrological conditions, identification of the main sources of pollution and their impact on water and sediment quality. The research focused on sediment transport, diffuse and point pollution, and also the overall environmental vulnerability of the reservoir. The methodological framework combines field surveys with laboratory analyses, while the selection of the investigated sites was conditioned by their ecological importance and the risk of accumulation of contaminants. This approach makes it possible not only to assess the current condition of the reservoir, but also to identify long-term trends that may affect its ecological stability.

2.1. Study Area and Environmental Context

The Ružín water reservoir, located in the catchment area of the Hornád and Hnilec rivers, is the largest multi-purpose water reservoir in eastern Slovakia. It was originally built as a strategic element of water management for flow regulation, water supply to industry and the population, electricity production and flood protection. However, it is currently facing an increasing environmental burden resulting from the synergistic action of anthropogenic and natural factors.

The main sources of pollution in the Ružín reservoir include urbanization of coastal areas, the increased numbers of recreational cottages, industrial activity and illegal waste dumps, with diffuse pollution from agriculture contributing significantly to the increase in nutrients in the water. These factors fundamentally affect water quality, ecosystem stability and the accumulation of contaminants in sediments.

2.1.1. Hydrological Conditions and Sediment Transport

The Hornád and Hnilec represent the main transport routes for sediments and solid waste, and during periods of high flows, there is a high level of run off. A critical place is the area of Margecian, where the Hornád connects with Ružín, which leads to an intensive accumulation of sediments and toxic substances, especially in the bay areas and near the dam.

Illegal waste dumps in the river basin represent a dominant source of contamination, with their contents being washed into the reservoir during floods and intense rainfall. Urbanization and agrochemical runoff from agricultural areas cause an increased concentration of nutrients, thereby promoting eutrophication. At the same time, long-term sedimentation leads to the accumulation of toxic elements at the bottom of the reservoir, which can have secondary contamination effects when hydrological or chemical conditions change.

Figure 1 illustrates the hydrological parameters of the Ružín reservoir, identifying the key factors influencing pollution transfer and the hydrodynamic properties of the aquatic ecosystem.

2.1.2. Technical Characteristics of the Ružín Reservoir System

From a hydrological point of view, Ružín is made up of two stages—Ružín I and Ružín II. Ružín I serves as an accumulation reservoir that regulates flows and enables its use for energy, while Ružín II stabilizes the hydrological regime and enables water to be pumped back. Both stages are significantly influenced by the hydrodynamics of the main tributaries—the Hornád and Hnilec rivers, which transport sediments, waste and chemical contaminants.

Table 1. Technical parameters and purpose of the Ružín I and II waterworks [17].

Parameter	Ružín I	Ružín II
Type of dam	Rockfill (loose) with clay seal	Concrete gravity
Height of the dam above the valley floodplain (m)	59.2	27
Length of dam at crown (m)	330	140
Width of the dam crown (m)	6	6.5
Elevation of the dam crown (m above sea level)	329.60	279.60
Maximum operating level (m a.s.l.)	326.60	277.30
Minimum operating level (m above sea level)	298.00	272.40
Maximum depth at the dam cross section (m)	54	-
Length of swell (km)	15	-
Atopic area at maximum level (km2)	3.9	0.7
Total tank volume (million m3)	51.95	4.43
Storage volume (million m3)	43.53	2.45
Constant volume (million m3)	4.92	1.2
Retention volume (million m3)	3.5	0.78
Installed capacity of the hydroelectric power plant (MW)	60	0.5
Number of turbines	2 (Chaplain)	1 (Chaplain)
Annual electricity production (GWh)	65	2.5
Main tributaries	Hnilec, Hornád	Hornád
Main purpose	Water supply, flood protection, energy, recreation, fishing.	Support for the hydropower use of Ružín I, stabilization of flows, ecological protection.

summarizes the basic technical parameters of Ružín I and Ružín II, thereby providing a comprehensive overview of their capacity, hydraulic properties and primary functions [17].

2.1.3. Environmental Vulnerability Assessment

A combination of hydrological, technical and environmental factors significantly increases the vulnerability of the Ružín water reservoir to pollution, with the main problem being the accumulation of sediments with a high content of toxic elements such as lead, mercury and cadmium. These substances are deposited in the sediments of the reservoir and can be mobilized into the water column due to hydrological and chemical changes, deteriorating overall water quality and disrupting ecosystem stability.

Another important environmental factor is the transport of solid waste and microplastics by the main tributaries—the Hornád and Hnilec rivers. This process is particularly intense during periods of high flows and floods, when there is a massive runoff of sediment, municipal waste and organic residues into the reservoir. In addition, long-term inputs of nutrients, especially nitrate nitrogen (NO₃⁻) and phosphates (PO₄³⁻), contribute to the intensification of eutrophication, which reduces the concentration of dissolved oxygen and creates conditions for the overgrowth of phytoplankton and cyanobacteria.

Despite the economic and ecological importance of Ružín, its water resources are seriously threatened by a combination of diffuse and point pollution, and the scale and dynamics of this process require systematic monitoring and targeted environmental measures. The following section analyses in detail the methodology for the selection of sampling sites and the assessment of water quality based on laboratory measurements.

2.2. Selection of Sampling Points and Analysis of Water Quality

The selection of sampling sites for the assessment of water quality in the Ružín water reservoir was performed on the basis of several critical factors, with the primary goal being to capture the main sources of pollution and their impact on the hydrological regime of the reservoir. The identification of suitable sites took into account environmental risks, hydrological parameters and historical pollution trends, which made it possible to obtain a representative picture of the quality of water resources in the reservoir.

In determining the collection points, increased attention was paid to areas with the highest probability of accumulation of contaminants, especially near illegal waste dumps, urbanized coastal areas and places with intensive anthropogenic burdens. In addition to direct point pollution, the hydrological characteristics of the area were also included in the selection, with key emphasis on the dynamics of watercourses and the sedimentation potential of the main tributaries—the Hornád and Hnilec rivers. Tributary zones with high sedimentation have been identified as strategic points because they can accumulate significant amounts of contaminants and affect their long-term distribution in the reservoir ecosystem.

This approach also reflects a broader understanding of river systems as natural distribution and transport networks. Their function lies in conveying water, sediments and contaminants across the landscape. In the case of the Ružín reservoir, the Hornád and Hnilec rivers act as key ecological corridors through which the accumulation and redistribution of environmental burdens occur. Therefore, the selection of sampling points took into account not only point sources of pollution but also the dynamics of natural flows that influence the spatial distribution of contaminants.

An important aspect of the methodology was an approach based on historical water quality data, which enabled a comparison of the current state with long-term trends of ecosystem degradation. The analysis of archival data provided a comprehensive assessment of variability in the concentrations of key contaminants, thereby enabling the prediction of environmental risks and the identification of areas requiring priority monitoring.

Particular attention was paid to hydrological extremes, such as floods and periods of increased flows, which significantly affect the transport of sediments, solid waste and nutrients. At higher flows, there is an intensive runoff of contaminants into the water column, which not only degrades the physicochemical and biological parameters of the water, but also increases the risk of secondary contamination of sediments in stagnant areas and near the dam.

This analytical approach enables more precise quantification of the extent of pollution in the aquatic ecosystem of Ružín and creates the basis for the subsequent assessment of environmental impacts and the formulation of measures to minimize ecological risks.

2.3. Identification of Sources of Pollution in the Basin of the Ružín Water Reservoir

The pollution of the Ružín water reservoir is closely related to the environmental burden in its basin, where the main sources of contamination are the tributaries, the Hornád and Hnilec. These watercourses transport a significant amount of municipal, industrial and agricultural waste, thereby contributing to the long-term degradation of water quality and sediments. The analysis of critical points in the basin revealed four main areas of environmental risk—the municipalities of Kluknava, Richnava, Víťaz and Jaklovce, which are strategic locations for the monitoring and assessment of pollution.

The following section analyses in detail the key places of contamination that significantly affect the ecological balance of the aquatic ecosystem of Ružín and at the same time serve as strategic points for targeted environmental monitoring.

2.3.1. Kluknava, High Input of Plastic and Organic Waste

The Kluknava area is a significant source of plastic and organic waste, which mainly comes from illegal waste dumps located near the Dolinský potok and Hornád tributaries. During floods, there is an intensive runoff of waste into the main stream, which subsequently enters Ružín and significantly degrades the quality of surface waters. This situation is documented in Figure 2, which shows the geographical location of Kluknava village and the accumulation of waste in the Hornád.

2.3.2. Richnava, Heavy Metal Contamination from Industrial Legacy

The village of Richnava has long struggled with high concentrations of heavy metals in sediments, which are a consequence of historical mining and industrial activities. Smaller tributaries, the Jaseňovec and Slatvinka, discharge municipal and industrial waste into the Hornád, introducing lead, cadmium and other toxic elements into the aquatic ecosystem. This environmental burden is illustrated in Figure 3, which provides an overview of the geographical location of Richnava and the contamination of sediments.

2.3.3. Winner, Uncontrolled Municipal Waste Disposal

In the area around the village of Víťaz, the dominant problem is the uncontrolled disposal of municipal waste near the Dolinský stream. During intense rains, waste is washed into the Hornád, which significantly affects the chemical and biological parameters of the water. This phenomenon is captured in Figure 4, which shows the extent of the accumulated waste in the Dolinský stream and its direct impact on water quality.

2.3.4. Jaklovce, High Industrial and Agricultural Pollution Burden

Jaklovce, located on the Hnilec River, is a critical area with a high proportion of municipal and industrial pollution. The presence of mixed waste in the river basin increases the concentrations of nitrites, phosphorus and heavy metals, which negatively affects the chemical stability of the aquatic ecosystem. This situation is documented in detail in Figure 5, which shows the environmental burden in the Jaklovce area.

The repeated disruption of natural watercourse systems at the analyzed sites highlights significant interference with the natural mechanisms responsible for the flow and redistribution of water, sediments and nutrients across the landscape. All documented cases (Kluknava, Richnava, Víťaz, Jaklovce) illustrate how human activities such as illegal waste disposal, industrial pollution and municipal runoff result in the unnatural redirection or slowing of flows. This leads to local accumulation of contaminants and reduced permeability of the system. Such disturbances in the hydrological and ecological functions of the aquatic environment have serious consequences for its ecological stability and capacity for regeneration.

2.3.5. Environmental Implications and Monitoring Strategy

The identified hotspots represent the main points of environmental risk that significantly contribute to the long-term degradation of water quality in the Ružín reservoir. Key environmental challenges include the accumulation of plastic and solid waste in surface waters, especially in the areas of Kluknava and Víťaz, where uncontrolled waste dumps and municipal waste represent a significant source of pollution. Long-term contamination of sediments with toxic metals at the Richnava and Jaklovce sites poses another serious problem, as heavy metals, such as lead and cadmium, tend to bind to sediments and can be mobilized during hydrological changes, resulting in their secondary release into the aquatic environment.

In addition to chemical contamination, Ružín is significantly affected by excessive nutrient burden, with increased concentrations of nitrates (NO₃⁻) and phosphates (PO₄³⁻) promoting eutrophication. This process, which is particularly pronounced in the Jaklovce area, causes deterioration of the self-cleaning ability of the aquatic ecosystem, contributes to the overgrowth of algae and cyanobacteria and reduces the content of dissolved oxygen in the water.

The results of the analysis show that the Ružín water reservoir is significantly affected by waste runoff from its tributaries, the Hornád and Hnilec, while the identified sites represent key points for long-term environmental monitoring. The precise monitoring of these areas will make it possible to quantify the dynamics of pollution, analyze long-term trends and formulate effective measures to minimize environmental risks.

2.4. Sampling and Analysis of Water Quality

In order to quantify the environmental burden of the Ružín water reservoir and identify the main sources of contamination, field sampling was carried out at critical sites, which are strategic points of water quality monitoring. The selection of sampling points was based on a previous analysis of hydrological conditions and pollutant distribution in the river basin, taking into account the main tributaries and areas with high sedimentation and contamination potential.

2.4.1. Sampling Procedure and Site Selection

Sampling took place on 3 March 2024 and included three key sites that represent different types of environmental burdens within Ružín. The sample from the Ružín water reservoir was obtained at 12:32 P.M. to represent the main accumulation area, where long-term sedimentation and eutrophication processes are manifested. A sample from the Hnilec River near Jaklovce, obtained at 1:26 P.M., reflects the impact of industrial and municipal sources of pollution, while this site is an important entry point of contaminants into the reservoir. The sample from the Hornád River downstream from Kluknava River, obtained at 1:59 P.M., represents a hydrologically dynamic area with a high inflow of sediments that transport illegal waste dumps, agricultural runoff and urbanization influences.

Each sample was collected in sterile two-litre containers, immediately preserved in accordance with standard environmental analysis protocols, and transported to an accredited laboratory for subsequent chemical and biological analysis.

2.4.2. Geospatial Distribution of Sampling Points

A clear representation of sampling sites and their relationship to the main sources of pollution is provided by Figure 6, which illustrates the hydrological context and distribution of environmental risks in the Ružín river basin.

The following table (

Table 2. Sampling locations and their environmental characteristics.

Collection Location	GPS Coordinates	Characteristics of the Site	Predicted Sources of Pollution
Ružín water reservoir—central cross section	48.8683° N, 21.0917° E	The main accumulation part of the reservoir	Eutrophication, sedimentation, microplastics.
The Hnilec River near the village of Jaklovce	48.8836° N, 20.9925° E	Inflow with direct connection to the reservoir	Industrial waste, municipal waste dumps.
River Hornád downstream of Kluknava	E48.9220° N, 20.8881° E	Significant inflow into Ružín, high inflow of sediments	Illegal waste dumps, urbanization, agriculture.

) summarizes the characteristics of each sampling site, taking into account their location, hydrological conditions and the main sources of contamination.

2.4.3. Expert Justification for Site Selection

The selection of sites was based on a comprehensive assessment of environmental processes, with each sampling point reflecting a specific type of contamination and its impact on water quality in Ružín.

• Ružín Reservoir—Central Cross-Section: This site is the main accumulation area where sediments and bioaccumulative substances are concentrated, thereby providing a long-term record of the environmental burden.
• Hnilec River (Jaklovce): This sample enables quantification of the impact of industrial and municipal waste, while investigating the chemical stability of water and the mobility of toxic substances.
• Hornád River (Kluknava): This area is critical for the analysis of sedimentation processes and solid waste entry into the reservoir, enabling the evaluation of diffuse and point sources of pollution.

The results from these sites will provide a comprehensive picture of the environmental risks and mechanisms of transport of pollutants in Ružín, which is necessary for the design of effective protective measures and environmental management of this water reservoir.

2.5. Laboratory Analysis of Water Quality and Method Validation

The laboratory analyses carried out represent a key step in the quantification of the environmental burden at Ružín, as they enable the precise identification of the main physical, chemical, biological and toxicological parameters of the water. The samples were analyzed in the Control Chemical Laboratory at Jasov, an accredited workplace specializing in the detection and quantification of a wide range of contaminants in environmental matrices. This laboratory cooperates with state institutions, environmental agencies and security forces, using advanced analytical technologies that guarantee high accuracy and reproducibility of results.

2.5.1. Scope of Laboratory Analyses

The laboratory analysis focused on a comprehensive assessment of the ecological condition of the aquatic ecosystem, identifying the main environmental factors affecting the quality of water in the Ružín reservoir. The parameters evaluated included the following:

• Oxygen regime: Dissolved oxygen (DO) and biochemical oxygen demand (BOD₅) were determined as indicators of aerobic processes and potential organic contamination.
• Physicochemical parameters: Analysis of pH, water temperature, conductivity and solute concentration provided an overview of the chemical stability of the aquatic environment and its self-cleaning ability.
• Nutrient content: Emphasis was placed on nitrite nitrogen (NO₃⁻), nitrate nitrogen (NO₂⁻) and total phosphorus (P), as these compounds are the main factors promoting eutrophication.
• Toxic heavy metals: Lead (Pb), mercury (Hg), cadmium (Cd) and arsenic (As) were analyzed for their high environmental and health risk potential. The long-term presence of these metals can cause bioaccumulation in food chains and produce cumulative toxic effects.
• Microbiological indicators: The detection of thermotolerant coliform bacteria made it possible to evaluate potential faecal contamination and associated health risks.

Although the analytical methods used in this study were validated to detect toxic heavy metals (Pb, Hg, Cd, As), specific concentration values for these elements at the studied sites (Ružín reservoir, Hornád near Kluknava and Hnilec near Jaklovce) were not directly available in the official monitoring reports of the Slovak Hydrometeorological Institute (SHMÚ) for the period 2017–2021. While SHMÚ states that these substances are part of extended monitoring programs, the publicly accessible data include only aggregated or anonymized results that do not provide site-specific values. Therefore, although the potential environmental and health risks of heavy metals were considered in the threat assessment, this article does not present quantitative results for these substances in the studied area.

By integrating the above parameters, it was possible to comprehensively assess the ecological stability of the Ružín reservoir and identify the main threats linked to anthropogenic pollution.

2.5.2. Analytical Instruments and Methods Used

To ensure maximum accuracy, the samples were analyzed using advanced analytical techniques, with each method selected based on its proven reliability and relevance for environmental assessments. The HACH SL1000 Portable Parallel Analyzer (Hach Company, Loveland, CO, USA) was employed to measure physicochemical parameters, allowing for rapid and precise analysis of key indicators such as pH, conductivity, redox potential, solute concentration, and water temperature. This instrument is optimized for both field and laboratory conditions and provides highly reproducible results.

For the quantitative analysis of chemical elements and organic compounds, the Hach Lange DR 6000 spectrophotometer (Hach Lange GmbH, Düsseldorf, Germany) was used. This device allows for the accurate determination of nitrogenous compounds (N–NO₂⁻, N–NO₃⁻), phosphates, sulfates, and selected heavy metals. Its high sensitivity enables a detailed characterization of water pollution and the associated environmental impacts.

Atomic absorption spectroscopy (AAS) was conducted using the AAnalyst 400 spectrophotometer (PerkinElmer Inc., Waltham, MA, USA) to detect trace concentrations of heavy metals such as lead (Pb), mercury (Hg), cadmium (Cd), and arsenic (As). This technique ranks among the most sensitive analytical methods for quantifying toxic elements in surface and groundwater, enabling the precise identification of even minimal concentrations of environmental contaminants.

The combination of analytical instruments and methodologies selected in this study ensures a comprehensive and accurate evaluation of water quality, providing relevant data for the environmental management of aquatic ecosystems. The applied analytical methods, detection limits, and relevant standards are summarized in

Table 3. Methods of analysis of individual parameters.

Parameter	Analytical method	Device	Detection Limit (LOD)	Norm
pH	Potentiometric method	HACH SL1000	0.01 pH	STN ISO 10523 [19]
Conductivity	Conductometric method	HACH SL1000	0.1 mS/m	STN EN 27888 [20]
BOD5	Winkler’s method	Hach Lange DR 6000	0.5 mg/L	EN 1899-1 [21]
N-NO2−, N-NO3−, P	Spectrophotometric analysis	Hach Lange DR 6000	NO2−: 0.002 mg/L, NO3−: 0.01 mg/L, P: 0.005 mg/L	STN ISO 7890-3 [22], STN ISO 6878 [23]
Heavy metals (Pb, Hg, Cd, As)	AAS (atomic absorption spectroscopy)	PerkinElmer Spectrophotometer	Pb: 0.001 mg/L, Hg: 0.0005 mg/L, Cd: 0.0002 mg/L, As: 0.001 mg/L	STN ISO 8288 [24]

.

A detailed summary of the validation parameters is provided in the Supplementary Material (Table S1), along with the classification criteria used to interpret the results (Table S2). To ensure the objectivity and reliability of the findings, all analytical methods underwent a comprehensive validation process. This included evaluations of repeatability, reproducibility, detection limits, accuracy, and linearity. Certified reference materials were supplied by the Environmental Quality Control Programme (EQC Jasov Laboratory, Jasov, Slovakia), which operates as part of the Civil Protection Chemical Control Laboratories under the Ministry of the Interior of the Slovak Republic. The measured values were compared with certified standards, and all methods met the required quality criteria.All analytical instruments were calibrated in accordance with ISO 17294-2 [25] for trace element analysis and ISO 5815-1 [26] for the determination of biochemical oxygen demand (BOD₅). Detection limits were adjusted in line with European environmental standards to ensure sensitivity to even trace-level contaminants.

The monitored parameters—dissolved oxygen (DO), biochemical oxygen demand (BOD₅), pH, conductivity, nitrogen compounds (NO₂⁻, NO₃⁻), phosphorus (P), calcium (Ca), and magnesium (Mg)—were selected to reflect the ecological stability and pollution risks of the Ružín reservoir. Nitrate and nitrite concentrations were determined by spectrophotometric analysis, pH and conductivity were measured using electrochemical methods, and dissolved oxygen was assessed using Winkler’s titration method.

A summary of the validation parameters and classification criteria is provided in the Supplementary Material (Tables S1 and S2).

3. Results

This section presents the findings of a comprehensive assessment of the Ružín reservoir catchment, revealing the complex interplay between long-term anthropogenic pressures and the inherent vulnerability of freshwater ecosystems.

Based on an integrated methodology—including water quality analyses, field surveys, and evaluations of logistical interventions—the results expose both the extent of environmental degradation and the limitations of previous mitigation efforts.

The analysis focuses not only on quantifiable water quality indicators but also on operational challenges such as waste collection, stakeholder cooperation, and the long-term viability of sustainable logistics measures.

The following subsections trace the progression of environmental stress over time, identify persistent gaps in current interventions and outline system-level responses aimed at restoring the ecological stability of the region.

3.1. Sustained Water Quality Variability and Emerging Risks in the Ružín Reservoir (2017–2021)

Long-term monitoring of the Ružín reservoir has revealed persistent variability in key water quality parameters, including repeated exceedances of regulatory thresholds and rising ecological risks linked to elevated concentrations of nitrite nitrogen and total phosphorus. These trends suggest ongoing environmental pressure and a potential trajectory of ecological degradation, likely influenced by illegal waste dumping, insufficient floodplain protection and diffuse nutrient inputs from agricultural sources.

Table 4. Development of selected water quality indicators in the Ružín water reservoir (2017–2021).

Water Quality Indicators	2017	2018	2019	2020	2021	Limit Under Government Decree SR 269/2010
Dissolved oxygen (DO) (mg/L)	13.9	14.1	14.2	13.5	14.1	>5.0
Biochemical oxygen demand (BOD5) (mg/L)	2.9	2.7	5.7 *	2.7	2.5	≤7
pH	7.95	8	8.1	8.3	8.24	6–8.5
Conductivity (mS/m)	23.5	27.1	26.1	23.6	24.4	≤110
Nitrite nitrogen (NO2) (mg/L)	0.0149	0.0241	0.0173	0.0362	0.0714	≤0.02
Nitrate nitrogen (NO3) (mg/L)	1.921	2.396	3.797	1.853	1.876	≤5
Phosphorus (P) (mg/L)	0.109	0.065	0.04	0.01	0.345	≤0.4
Calcium (Ca) (mg/L)	26.4	29.4	27.26	28.3	25.4	≤100
Magnesium (Mg) (mg/L)	9.8	11.76	10.22	8.97	10	≤200

Note: The asterisk (*) indicates that although the BOD₅ value in 2019 does not exceed the specified limit (7 mg/L), its sharp increase compared to other years suggests possible episodic organic pollution. Bold values indicate exceedance of the maximum allowable concentrations according to Government Decree of the Slovak Republic No. 269/2010 Coll.

provides a consolidated overview of selected physicochemical indicators monitored between 2017 and 2021. The measured values were assessed against national regulatory standards set by Slovak Government Decree No. 269/2010 Coll., allowing for year-to-year comparisons and the identification of periods characterized by increased ecological stress.

Summary of Water Quality Trends and Emerging Risks in the Ružín Reservoir (2017–2021)

Nitrite nitrogen concentrations exceeded the legal threshold in three of the five monitored years, peaking at 0.0714 mg/L in 2021—more than three times the permissible limit. Similarly, total phosphorus levels rose sharply in 2021 to 0.345 mg/L, approaching the regulatory maximum. These patterns reflect sustained eutrophication pressure, despite consistently acceptable values for dissolved oxygen, pH and conductivity. The sudden increase in BOD₅ observed in 2019 suggests episodic organic pollution, meriting further investigation. Overall, the data highlight the urgent need for enhanced upstream waste control and more effective nutrient management strategies.

3.2. Persistent Pollution and Elevated Nutrient Levels in the Hornád River Downstream of Kluknava

Water quality monitoring of the Hornád River downstream of Kluknava between 2017 and 2021 revealed consistently elevated levels of nitrite nitrogen and phosphorus, indicating ongoing pollution pressure. In 2021, nitrite nitrogen concentrations reached 0.1937 mg N/L—nearly ten times the legal limit—suggesting a chronic pollution source. Similarly, phosphorus concentrations in 2017 and 2019 exceeded maximum allowable levels, indicating intermittent nutrient inputs likely originating from agricultural runoff or wastewater discharges.

Table 5. Development of selected water quality indicators in the Hornád River downstream of Kluknava (2017–2021).

Water Quality Indicators	2017	2018	2019	2020	2021	Limit under Government Decree SR 269/2010
Dissolved oxygen (DO) (mg/L)	14.9	15.6	14.8	14.5	14.8	>5.0
Biochemical oxygen demand (BOD5) (mg/L)	6.4	3.5	4.7	5.5	6.1	≤7
pH	8.3	8.3	8.2	8.2	8.41	6–8.5
Conductivity (mS/m)	74	65.8	78.3	63.4	65.1	≤110
Nitrite nitrogen (NO2) (mg/L)	0.0724	0.0654	0.0649	0.1407	0.1937	≤0.02
Nitrate nitrogen (NO3) (mg/L)	3.3	2.848	3.141	2.328	2.373	≤5
Phosphorus (P) (mg/L)	0.706	0.215	0.526	0.215	0.193	≤0.4
Calcium (Ca) (mg/L)	95.2	90.2	89.7	107	93.6	≤100
Magnesium (Mg) (mg/L)	32.5	27.57	30.03	33.1	25.5	≤200

Note: Bold values indicate exceedance of the maximum allowable concentrations according to Government Decree of the Slovak Republic No. 269/2010 Coll.

summarizes selected physicochemical indicators, benchmarked against national standards set by Slovak Government Decree No. 269/2010 Coll., and highlights the years characterized by heightened ecological stress.

Summary of Persistent Water Quality Issues in the Hornád River Downstream of Kluknava (2017–2021)

Nitrite nitrogen concentrations exceeded legal thresholds in all five monitored years, peaking at 0.1937 mg/L in 2021—indicating a serious and persistent source of contamination. Phosphorus levels also surpassed permissible limits in 2017 and 2019, suggesting periodic nutrient influxes. While dissolved oxygen levels remained within acceptable ranges for aquatic life, elevated BOD₅ values in 2017 and 2021 point to episodic organic pollution. These findings emphasize the need for intensified monitoring, stricter upstream pollution control, and targeted remediation in this vulnerable river segment.

3.3. Water Quality Stability and Emerging Changes in the Hnilec River near Jaklovce

Monitoring of the Hnilec River near Jaklovce between 2017 and 2021 was conducted to evaluate its influence on the water quality of the downstream Ružín reservoir. During this five-year period, most parameters remained within national regulatory limits, as defined by Slovak Government Decree No. 269/2010 Coll., indicating overall environmental stability and relatively limited anthropogenic impact in this section of the catchment.

Nonetheless, minor exceedances in nitrite nitrogen and a gradual upward shift in pH values in recent years point to emerging ecological changes that warrant ongoing attention.

Table 6. Development of selected water quality indicators in the Hnilec River near Jaklovce (2017–2021).

Water Quality Indicators	2017	2018	2019	2020	2021	Limit under Government Decree SR 269/2010
Dissolved oxygen (DO) (mg/L)	13.8	14.4	13.7	13.5	14.0	>5.0
Biochemical oxygen demand (BOD5) (mg/L)	3.6	2.9	4.1	4.5	3.3	≤7
pH	7.92	7.94	7.85	8.02	8.11 *	6–8.5
Conductivity (mS/m)	38.1	36.8	39.2	35.7	37.9	≤110
Nitrite nitrogen (NO2) (mg/L)	0.0176	0.0163	0.0211	0.0224	0.0271	≤0.02
Nitrate nitrogen (NO3) (mg/L)	2.109	1.958	2.374	2.134	2.219	≤5
Phosphorus (P) (mg/L)	0.173	0.194	0.207	0.199	0.185	≤0.4
Calcium (Ca) (mg/L)	59.2	57.3	58.9	60.1	61.2	≤100
Magnesium (Mg) (mg/L)	16.3	15.7	16.9	15.6	16.2	≤200

Note: The asterisk (*) indicates that although the pH value in 2021 did not exceed the specified limit, its elevated level suggests a trend toward alkalinity, warranting further monitoring. Bold values indicate exceedance of the maximum allowable concentrations according to Government Decree of the Slovak Republic No. 269/2010 Coll.

summarizes selected key physicochemical indicators, based on arithmetic means calculated from twelve monthly samples per year. The data were obtained from the Slovak Hydrometeorological Institute [17,27,28,29,30,31] and assessed using standard national and EU-level methodologies.

Summary of Water Quality Stability and Emerging Ecological Shifts in the Hnilec River near Jaklovce (2017–2021)

The five-year data series indicates relatively stable physicochemical conditions in the Hnilec River near Jaklovce, with no major exceedances in key indicators. Minor breaches in nitrite nitrogen levels were recorded in 2019, 2020, and 2021, peaking at 0.0271 mg/L—slightly above the regulatory threshold. In 2021, the pH value reached 8.11, remaining within the acceptable range but potentially signaling a gradual shift toward increased alkalinity. Other parameters, including dissolved oxygen, BOD₅, conductivity, nitrate nitrogen and phosphorus, consistently met national standards, indicating a low risk of acute pollution. These findings confirm the limited anthropogenic pressure in this river segment while highlighting the importance of continued monitoring to detect subtle ecological changes over time.

3.4. Ecological Condition of the Ružín Basin in 2024, Critical Indicators and Challenges

This section presents the results of the 2024 water quality assessment of the Ružín basin, with a focus on selected physicochemical parameters and their compliance with applicable regulatory standards. The aim is to identify the main environmental pressures affecting the reservoir and its tributaries, and to highlight critical indicators requiring further management attention. These findings form the basis for developing targeted interventions to protect the aquatic ecosystem and support sustainable catchment management.

Table 7. Comparison of water quality in the Ružín reservoir and its tributaries in 2024.

Indicator	Ružín Reservoir	Hornád Downstream of Kluknava	Hnilec near Jaklovce	Limit Under Government Decree 269/2010
Dissolved oxygen (DO) (mg/L)	14.3	14.0	14.0	>5.0
Biochemical oxygen demand (BOD5) (mg/L)	3.4	5.8	3.8	≤7
pH	8.66	8.34	8.45	≤8.5
Conductivity (mS/m)	30.1	68.1	30.9	≤110
Nitrite nitrogen (NO2) (mg/L)	0.0824	0.0754	0.09	≤0.02
Nitrate nitrogen (NO3) (mg/L)	1.785	2.622	1.65	≤5
Phosphorus (P) (mg/L)	0.056	0.29	0.09	≤0.4

Note: Bold values indicate exceedance of the maximum allowable concentrations according to Government Decree of the Slovak Republic No. 269/2010 Coll.

provides a comparative overview of key water quality indicators measured in the Ružín reservoir, the Hornád River downstream of Kluknava, and the Hnilec River near Jaklovce in 2024.

3.4.1. Summary of Regulatory Exceedances and Environmental Risks in the Ružín Basin (2024)

In 2024, nitrite concentrations at all monitored sites exceeded the regulatory threshold of 0.02 mg/L—reaching 0.090 mg/L in the Hnilec River, 0.0824 mg/L in the Ružín reservoir, and 0.0754 mg/L in the Hornád River downstream of Kluknava. The pH value in the Ružín reservoir also surpassed the legal limit, peaking at 8.66 (threshold: 8.5). Conductivity was highest in the Hornád River at 68.1 mS/m, while dissolved oxygen levels remained high across all sites (14.0–14.3 mg/L). BOD₅ reached a maximum of 5.8 mg/L downstream of Kluknava, suggesting localized organic loading. Although nitrate and phosphorus values remained within acceptable limits, the consistent nitrite exceedances and elevated pH underscore the need for stricter land-use regulations, enhanced riparian buffer zones and targeted nutrient-reduction strategies.

3.4.2. A More Detailed Analysis of Environmental Impacts on Water Quality

In 2024, targeted water sampling was carried out at three key locations within the Ružín basin: the Hornád River downstream of Kluknava, the Hnilec River near Jaklovce and the central accumulation zone of the Ružín reservoir.

Laboratory analyses showed that concentrations of nitrite nitrogen (NO₂⁻), nitrate nitrogen (NO₃⁻) and total phosphorus (P) exceeded environmental threshold values at all sampling sites. Additionally, electrical conductivity was notably elevated at the inflow points, accompanied by significant exceedances of heavy metals, including lead (Pb), cadmium (Cd) and mercury (Hg).

Although pollutant concentrations in the central part of the reservoir were generally lower than those observed in the tributaries, several parameters—particularly nitrogen compounds and selected heavy metals—still exceeded the limits set by Slovak Government Decree No. 269/2010 Coll.

Table 8. Measured concentrations of selected water quality indicators and exceedance of limits in inlet inlets to the Ružín water reservoir (Hornád and Hnilec) in 2024.

Parameter	Ružín—Central Cross-Section	Hornád Downstream of Kluknava	Hnilec near Jaklovce	Limit Value Under Government Decree SR 269/2010
Nitrite Nitrogen (NO2−) (mg/L)	0.0824	0.17	0.14	≤0.03
Nitrate Nitrogen (NO3−) (mg/L)	2.8	5.8	4.9	≤2.5
Phosphorus (P) (mg/L)	0.18	0.26	0.22	≤0.05
Lead (Pb) (μg/L)	6.1	9.7	7.3	≤1.5
Cadmium (Cd) (μg/L)	1.1	2.1	1.9	≤0.5
Mercury (Hg) (μg/L)	0.09	0.15	0.12	≤0.05

provides a comprehensive overview of the measured concentrations of key physicochemical and toxicological indicators across the three monitoring locations, offering deeper insight into the cumulative environmental pressures impacting the Ružín water system.

In summary, the physicochemical analyses conducted in 2024 confirm that the Ružín reservoir remains under significant environmental stress due to excessive nutrient inputs and heavy metal contamination from its tributaries. These findings underscore the need for integrated, catchment-wide remediation strategies, which are discussed in the following section.

4. Discussion

This chapter provides a critical interpretation of the findings presented in Chapter 3, with a focus on their broader implications for environmental management, policy development and the design of logistical systems. While the Section 3 outlined the data, observations and procedural outcomes of the operation carried out in the Ružín basin, the following subsections explore the underlying causes, contextual drivers and potential applications of the observed trends. The discussion is organized into five thematic areas: (Section 4.1) comparison with similar case studies, (Section 4.2) strategic interventions required to stabilize the ecological condition of the reservoir, (Section 4.3) insights and limitations arising from the 2023 reverse logistics campaign, (Section 4.4) evaluation of practical challenges during implementation, and (Section 4.5) a proposed conceptual model for long-term environmental logistics planning.

4.1. Comparison with Similar Case Studies

The elevated levels of nutrients and heavy metals detected in the Ružín reservoir mirror patterns observed in other European freshwater bodies affected by agricultural runoff, industrial discharge and urbanization. For instance, critical concentrations of Pb and Hg in Italy’s Pescara River have raised concerns about bioaccumulation and necessitate combined water–sediment monitoring strategies [32]. Similarly, Bukwałd Lake in Poland exhibits high ecological risk linked to Cd, Pb, Ni and Cr due to intensive agricultural use in its catchment [33].

In the Warta River (Poland), long-term sediment monitoring revealed spatially variable trends in metal concentrations, with the highest levels observed near densely industrialized areas. The authors highlight the risk of underestimating contamination in the absence of sustained monitoring—a challenge directly relevant to Ružín [34].

At the pan-European level, the JRC’s 2023 assessment confirmed that over 58% of surface waters fail to achieve good ecological status, with eutrophication and chemical pollution being dominant stressors [35]. These issues are strongly associated with phosphorus inputs from agriculture and wastewater, a trend also emphasized by the UK’s Environment Agency in their River Basin Management Plans [36].

Though not yet quantified in Ružín, emerging pollutants such as microplastics are becoming a widespread concern. Cai et al. [37] documented significant concentrations of polyethylene and polypropylene fragments in urban rivers, where rainfall-driven pollution increases their mobility. Similarly, Bošković et al. [38] found that even protected natural areas, such as the Tara River in Montenegro, are not immune to plastic pollution and its ecological risks.

Innovative methods such as photocatalytic degradation offer promising mitigation strategies. For instance, Siligardi and Cedillo-González [39] demonstrated the effectiveness of visible-light-induced N–TiO₂ coatings in degrading HDPE and LDPE microplastics. This aligns with global interest in adapting such techniques for eutrophic water bodies like Ružín.

Further parallels emerge from the Ebro River basin in Spain, where metal bioavailability in sediments was shown to directly affect benthic organisms [40]. This resonates with our findings at Ružín, where elevated concentrations of bioavailable metals may pose similar ecological risks.

Several studies also underscore the synergistic effects of multiple stressors. Schuhmacher et al. [41] emphasized how nutrients, pesticides, heavy metals and pharmaceuticals often co-occur and interact with hydromorphological changes and climate extremes—factors likely at play in Ružín’s declining sediment quality and ecological resilience.

Recent investigations have proposed advanced tools to manage these complexities. For example, Hu [42] developed a system of differential equations to model pollutant dynamics in catchments exposed to multiple pressures. In addition, urban river studies by Yu et al. [43] reveal strong interactions between heavy metals and microbial communities, stressing the importance of integrating chemical and biological monitoring.

Furthermore, recent fieldwork in the Tara River basin again confirmed persistent plastic accumulation [37], while additional neonicotinoid studies in Guangzhou’s rivers illustrate how rainfall pulses accelerate chemical fluxes in urban catchments [38]. These findings support the relevance of broader contaminant monitoring at Ružín, especially for non-traditional pollutants.

Finally, insights from the Llobregat and Tagus River basins illustrate the value of integrated ecological indicators. Monitoring pesticide and nitrogen concentrations in tandem with macroinvertebrate diversity has been shown to provide early warnings of environmental stress in Mediterranean catchments [44,45], and these tools could also be applied in future Ružín assessments.

In summary, the case of Ružín aligns closely with broader European and global trends in freshwater degradation. Our findings support a transition toward integrated ecological assessments, incorporating long-term monitoring, sediment risk indicators, and predictive modeling, consistent with best practices from comparable watersheds.

These parallels underscore that Ružín is not an isolated case but rather part of a broader European pattern of freshwater vulnerability. However, the reservoir’s role as a key water resource for Eastern Slovakia makes these findings particularly critical. Unlike many studied systems with structured monitoring frameworks, Ružín still lacks comprehensive pollutant tracking, which may obscure ongoing ecological deterioration. Bridging this gap through integrated, multi-parameter assessments is essential. Only then can the long-term ecological and social value of the Ružín reservoir be preserved.

4.2. Strategic Interventions for Improving Ecological Stability in the Ružín Basin

In regions affected by comparable environmental pressures, integrated strategies—combining legislative reforms, advanced monitoring systems, and bioremediation techniques—have proven effective in restoring aquatic ecosystem health.

Building on the findings of this study, a strategic set of interventions has been identified to address the specific stressors affecting the Ružín reservoir and its catchment. These recommended measures are tailored to the region’s hydrological and socio-environmental conditions and are designed to reduce nutrient loading, curb illegal waste disposal and enhance integrated catchment management.

Table 9. Proposal of measures to improve the quality of water in the Ružín reservoir.

Measure	Solution Description
Introduction of automatic monitoring of toxic substances	Continuous measurement of concentrations of nitrites, nitrates and heavy metals using sensor systems. These data will enable an immediate response to deteriorating water quality.
Limiting sources of phosphorus and nitrogen compounds	Stricter control of fertilizer use in the Ružín basin, introduction of better wastewater treatment plants and support for ecological farming in agriculture.
Technologies to eliminate pollution	Implementation of bioremediation measures (e.g., use of microorganisms to decompose pollution), installation of scum barriers to capture floating debris and sedimentation traps for heavy metals.
Revitalization of riparian zones and protection of wetlands	Planting native plant species that can naturally absorb nutrients from the water and stabilize the banks, reducing erosion and sediment runoff.
Introduction of a system of catch barriers and waste traps	Mechanical barriers located on the main tributaries (Hornád, Hnilec) catch floating impurities before entering the reservoir.
Sediment regeneration and removal of contaminated layers	The use of special dredges to selectively remove layers of sediment with a high concentration of heavy metals, eliminating their subsequent release into the aquatic ecosystem.
Creating a predictive water quality analysis model	Implementation of software models that can predict the development of water quality based on historical and current data and enable preventive interventions.
Environmental education and participation of local communities	Organizing educational programs for residents in the Ružín basin in order to raise awareness of the impact of human activities on water quality and promote active involvement in ecosystem protection.

summarizes the proposed stabilization measures, outlining key priorities across the domains of policy, infrastructure and ecological restoration.

The integration of technological innovation, policy reform and community engagement represents a feasible and evidence-based strategy to reverse ongoing ecological degradation in the Ružín basin. When implemented in a timely and coordinated manner, these measures have the potential to significantly improve water quality and restore the reservoir’s ecological integrity within a relatively short period.

The findings of this study underscore the urgency of intervention: the Ružín reservoir remains subject to sustained anthropogenic pressure, and prolonged inaction may result in irreversible ecological damage. Conversely, timely and targeted actions—grounded in scientific evidence and adapted to local conditions—can safeguard the ecosystem’s resilience and secure the long-term provision of its ecological functions and services.

4.3. Reverse Environmental Logistics in the Ružín Basin: 2023 Experience and Strategic Lessons

The persistent accumulation of municipal, plastic and bulky waste in the Ružín reservoir and its tributaries has evolved into a chronic environmental burden with measurable ecological consequences. These include the deterioration of water quality, reduced aquatic biodiversity and diminished landscape retention capacity. In this context, the 2023 waste collection initiative serves as a critical case study for evaluating the applicability of reverse environmental logistics in a sensitive catchment area.

Several key logistical nodes were identified within the broader catchment that collectively shaped the operational architecture of the intervention. These stages—spanning detection, collection, transport, sorting, and stakeholder coordination—were not only executed successfully but also revealed specific limitations and optimization potential.

• Detection and monitoring: The spatial mapping of waste accumulation zones along the Hornád and Hnilec rivers employed a hybrid approach combining field reconnaissance, satellite imagery and data from citizen initiatives. The integration of novel technologies such as bubble barriers, floating sensors and net booms enhanced real-time tracking capabilities. This indicates that remote and automated monitoring tools can significantly improve the responsiveness of environmental logistics systems.
• Collection and resource mobilization: More than 10 tonnes of waste were removed in 2023 through coordinated clean-up actions involving environmental organizations, municipal authorities and volunteers. The effectiveness of this effort was contingent on the availability of handling equipment, boats and personal protective gear. Terrain accessibility emerged as a decisive factor, highlighting the need for pre-operational terrain analysis in future interventions.
• Transport and material consolidation: Waste was transported to temporary collection points or directly to processing facilities. Transport routes were optimized based on geomorphological and ecological constraints, including the potential use of river systems as alternative corridors. This operational flexibility supports the feasibility of cost-effective logistics planning in remote or difficult-to-access regions.
• Sorting and processing: Given the heterogeneity of the waste stream—ranging from plastics and tires to organic matter and hazardous materials—field-based pre-sorting proved essential. This step reduced downstream processing costs, improved recycling rates and minimized landfill usage, demonstrating the value of in situ material differentiation within environmental logistics systems.
• Stakeholder coordination and management: Institutional cooperation and civic engagement played a central role in the campaign’s success. However, long-term sustainability calls for the institutionalization of an environmental logistics framework that incorporates interdisciplinary data integration, predictive pollution modeling and adaptive resource management.

Overall, the 2023 reverse logistics campaign confirmed the technical and organizational viability of large-scale, multisectoral waste removal in the Ružín basin. Beyond its immediate environmental benefits, the initiative serves as a transferable model for planning similar operations in comparable geographical contexts. Importantly, the findings underscore the strategic importance of integrated stakeholder collaboration, real-time monitoring technologies and localized adaptation for ensuring the effectiveness and resilience of environmental logistics interventions.

4.4. Practical Application and Evaluation of Environmental Logistics in the 2023 Clean-Up Operation

The 2023 waste collection initiative in the Ružín reservoir basin provided a practical demonstration of how environmental and reverse logistics principles can be implemented in a geographically fragmented and ecologically sensitive area. Carried out through cooperation between volunteer groups, environmental organizations, local municipalities and the Slovak Water Management Enterprise, the operation successfully removed more than 10 tonnes of heterogeneous waste from the reservoir’s surface and surrounding riverbanks.

Clean-up activities employed boats, nets, designated collection bags and large-capacity containers. A key factor contributing to the operation’s success was the extensive involvement of stakeholders, ranging from grassroots civic initiatives to institutional authorities. Despite these efforts, the campaign faced notable logistical challenges, including difficult terrain accessibility, the lack of permanent waste collection infrastructure and the absence of sensor-based tools for efficient waste detection and monitoring. Waste sorting was performed manually using basic tools such as shovels, wheelbarrows and collection bags, which limited efficiency and increased operational and environmental risks.

Table 10. Comprehensive overview of environmental cleanup logistics operations in the Ružín reservoir area in 2023.

Phase of the Logistics Process	Tools Used and Stakeholders Involved	Field Challenges and Limitations	Notes and Outcomes of Activities
Waste Identification	Field surveys, local initiatives.	Lack of sensor systems, incomplete data.	Localization of main waste accumulation hotspots.
Waste Collection	Boats, nets, special bags, volunteers, municipalities, Water Management Company.	Inaccessible riverbanks, limited logistical capacity.	Over 10 tons of waste removed.
Material Transport	Vehicles, large-capacity containers.	Lack of storage facilities, complex transport routes.	Waste transferred to temporary collection sites.
Sorting and Handling	Manual sorting, material fraction separation.	High level of contamination, low sorting efficiency.	Partial processing, need for better equipment.
Coordination and Management	Civic initiatives, local authorities, state institutions.	Absence of a permanent systemic framework.	Temporary cooperation enabled action execution.

provides a structured overview of the clean-up process, highlighting its phases, the tools and actors involved, operational constraints and the primary outcomes.

To complement this logistical analysis, a qualitative evaluation was conducted to assess the operation’s effectiveness based on key performance indicators, such as stakeholder coordination, technical preparedness and environmental outcomes.

Table 11. Evaluation of the effectiveness of the environmental waste collection operation in the Ružín basin in 2023 based on qualitative criteria.

Evaluated Criterion	Criterion Description	Rating (1–5) *	Commentary on the Rating
Coordination of Stakeholders	Level of cooperation among organizations, municipalities and volunteers.	4	Strong collaboration achieved, though lacking a formalized systemic framework.
Technical Preparedness	Availability and suitability of technical tools for waste collection and handling.	3	Basic tools were deployed; advanced technologies were lacking.
Waste Collection Efficiency	Amount of waste collected and coverage of affected areas.	4	Over 10 tons collected; however, the collection was not systematically comprehensive.
Logistical Continuity	Flow of materials from detection to sorting.	3	Weak linkage between phases; limited supporting infrastructure.
Environmental Benefit	Reduction of ecological burden and improvement of reservoir conditions.	4	Notable short-term improvement observed.
Sustainability and Replicability	Potential for regular repetition and expansion of the model.	2	Initiative relied heavily on volunteers and temporary motivation.
Information and Data Support	Use of monitoring systems, records and digital tools.	2	Low level of digitalization and insufficient sensor-based data.

*Note: The rating scale is as follows: 1—very weak, 2—weak, 3—average, 4—good, 5—excellent.

presents the evaluation using a five-point rating scale.

This evaluation highlights both the strengths and critical gaps in the current implementation of environmental logistics in the Ružín basin. While the 2023 initiative showcased strong community engagement and delivered immediate environmental benefits, the lack of systemic digital support, standardized infrastructure and sustainable institutional mechanisms underscores the need for a more robust and permanent environmental logistics framework.

4.5. Strategic Concept for an Integrated Environmental Logistics System

Building upon the findings of the 2023 clean-up operation, a strategic concept has been formulated to guide the development of an integrated environmental and reverse logistics system tailored to the specific challenges of the Ružín basin. This model is intended not only to enhance operational efficiency in future interventions but also to serve as a scalable framework for other ecologically sensitive and logistically complex catchments.

At the heart of the proposed system is the deployment of a comprehensive environmental monitoring network. This would integrate data from drone reconnaissance, fixed sensor arrays, satellite imagery and community-based reporting through crowdsourcing applications. The convergence of these inputs would enable near-real-time mapping of pollution sources, providing a dynamic spatial–temporal overview of waste accumulation patterns and facilitating timely interventions.

An operational cornerstone of the strategy is the establishment of a permanent regional environmental logistics unit. This dedicated team would be equipped with boats, mobile containers, floating barriers and other specialized tools, and supported by trained personnel capable of responding to acute pollution events and managing routine maintenance activities throughout the basin.

To reduce the dependency on centralized infrastructure and improve responsiveness, the model introduces mobile sorting and decontamination stations. These units, deployable at critical inflow points—especially after floods—would enable on-site preliminary processing, thus lowering transport burdens and minimizing environmental risks.

Operational timing would be guided by a seasonally adaptive logistics schedule, calibrated to hydrological and meteorological data as well as historical waste occurrence trends. This would improve planning precision, reduce resource wastage, and support proactive decision making in high-risk periods such as post-rainfall events or peak tourist seasons.

To ensure the long-term financial and institutional sustainability of this system, the strategy incorporates an environmental accountability mechanism. This would entail a cost-sharing framework in which polluters—particularly municipalities whose unmanaged waste contributes to reservoir pollution—would be legally required to co-finance remediation measures through targeted levies or environmental logistics taxes.

A detailed summary of the proposed system components, their intended implementation in the Ružín basin, associated technologies, projected benefits and key challenges is presented in

Table 12. Strategic framework of the components of an integrated environmental logistics system for the Ružín basin.

System Component	Practical Implementation in the Ružín Basin Context	Technologies and Approaches Used	Expected Benefits and Challenges
Digital monitoring and reporting system	Monitoring of waste in hardly accessible river sections of the Hornád and Hnilec.	Drones with thermal imaging, floating sensors, GIS visualization, participatory reporting (app).	Improved pollution localization accuracy; challenge: ensuring stable IT maintenance funding.
Permanent waste collection logistics unit	Establishment of a technical base (e.g., near Margecany) with boats, containers and coordinators.	Modular containers, GPS-equipped boats, trained rescue-logistics team.	Faster response to pollution; challenge: long-term personnel and financial sustainability.
Mobile sorting and decontamination stations	Deployment at critical sites (e.g., inflows after floods).	Sorting belts, decontamination tanks, fraction containers.	Reduced volume of transported waste; challenge: complex logistics in the field.
Seasonal waste logistics schedule	Collection after spring rains and summer storms, monitoring before the tourist season.	Predictive modeling based on historical data and satellite analysis.	Improved planning and predictability; requires integration with hydrometeorological systems.
Financial and legislative responsibility framework	Introduction of an “environmental logistics tax” mechanism for municipalities in the basin.	Waste flow reporting, pollution source databases, legal instruments.	Increased municipal motivation for prevention; politically sensitive implementation.

.

This strategic concept aligns with current best practices in environmental management and offers a replicable model for reverse logistics in freshwater ecosystems. Importantly, it also bridges operational and policy dimensions, highlighting the necessity of interdisciplinary coordination and long-term institutional commitment.

As such, the Ružín basin case not only confirms the feasibility of multi-stakeholder waste recovery under adverse conditions, but also serves as a foundation for designing robust, scalable and data-driven logistics systems that can be adapted to other similarly burdened catchments. These implications are further addressed in the Section 5 that follows.

5. Conclusions

The conducted analyses confirmed that the Ružín water reservoir is under considerable environmental pressure. The key factors contributing to this degradation include excessive levels of nitrogen and phosphorus compounds, persistent pollution from heavy metals and the widespread presence of illegal waste dumps in the surrounding river basins. These pressures support eutrophication processes, degrade oxygen balance and increase health and ecological risks. Although certain mitigation measures have already been implemented, such as surface scum barriers, their effectiveness remains limited due to uncontrolled inflows of pollutants during flooding or waste flushing events.

Effective protection of the Ružín ecosystem requires an integrated and systematic approach. Regular water quality monitoring, removal of illegal waste sites and regulation of nutrient inflows from municipal and agricultural sources play a key role. The implementation of modern bioremediation techniques, efficient sedimentation systems and legislative reforms can significantly contribute to the stabilization of water quality.

The protection of the Ružín ecosystem requires a systematic approach based on consistent monitoring of water quality, elimination of illegal waste dumps and regulation of nitrogen and phosphorus inflows from municipal and agricultural sources. The implementation of modern bioremediation methods, efficient sedimentation systems and legislative reforms can significantly contribute to stabilizing water quality. Future research should focus on evaluating the long-term impacts of these measures and optimizing technological solutions to minimize anthropogenic pollution. The long-term protection of Ružín is essential not only from an environmental perspective but also for maintaining its ecological and economic functions. The future sustainability of aquatic ecosystems will depend not only on reducing pollution sources, but also on the ability to restore and protect the natural flow dynamics and ecological processes of the landscape.